In the prior art techniques for grinding materials, a great diversity of well known systems and processes are used, among which there may be mentioned those that are based on the impact of certain mechanical members of the grinders (such as in hammer mills) and the particles of the material which is to be ground, in order to break said particles until the desired fineness is obtained, as well as those in which the materials are impacted against particles of very hard materials (such as in ball mills), in order to achieve the grinding of said particles of material, and also those which operate by rubbing or attrition (attrition or rubbing mills) wherein a pair of mill wheels or grind stones are rubbed against each other and against the particles of the material in order to comminute the same.
In more recent times other types of grinding systems have been developed wherein apparatus are provided which are capable of building up a layer of the same material on the impact surfaces thereof, such that the moving particles of the material will impact, not against the moving members of the grinder but, on the contrary, against the layers of material formed and deposited thereon, whereby the duration of the operational members of the grinders is greatly increased, inasmuch as in this instance the particles of material to be ground are impacted against temporary layers previously built up with the material which is being ground, thereby effecting the grinding operation through impacts of the materials themselves, rather than through impact of said materials against abradable members of the grinder.
Finally, grinding systems are also known wherein the grinding principle is to throw the particles of material by means of high pressure air or gas, either against other particles of the material or against rigid working surfaces of the grinder.
The problems caused by the prior art grinding systems wherein the materials impact against rigid working members, either moved by the same apparatus or loose and thrown by some type of special system, are very well known and essentially reside in the low life of the working members, which must be replaced very frequently, inasmuch as the abrasive action of the materials under treatment, causes a very fast wear of said members, with the consequent economical disadvantages caused both by the replacement of said members and by the stops of the machine caused thereby.
The introduction of grinding systems in which the materials are made to impact against layers of the same material deposited on working moving surfaces, considerably improved the conditions of operation and solved the drawbacks shown by the traditional prior art grinders wherein the materials are impacted against rigid working members, inasmuch as it is the same material which receives said impact of the particles under treatment and, therefore, there is no substantial wear of the materials of which the grinder is built. However, this type of systems may be generally regarded as of a slow speed, inasmuch as the speed that may be given to the moving layers of materials is limited, in view of both static and dynamic equilibrium considerations, inasmuch as the material layers built up over the moving working surfaces, cause unequal forces that provoke high vibration of the apparatus. Therefore, it was materially impossible to solve the above problem of slow operation merely by means of increasing the speed of the moving layers of material, because the dynamic equilibrium considerations were mandatory in this type of systems and it was not possible to increase the speed indefinitely.
Therefore, a grinding principle has been for long sought that might solve the problems caused by the abrasion of the working surfaces of the grinders and, while these problems were partially solved by means of the principle which involves the building up of layers of the same material on the surfaces of the grinders which otherwise would be worn out, the solution was not quite appropriate, because a slowness factor was incorporated. Consequently, it has been the aim of the workers dealing with this problem, to device a system in order to considerably increase the speed of said working layers of material, so as to produce a very fast and easy grinding operation, without any success up to the present date.